P0038
1NZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0037: Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
DTC P0037 - Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
DTC P0038 - Oxygen Sensor Heater Control Circuit High (Bank 1 Sensor 2)
DTC P0141 - Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
DESCRIPTION
A three-way catalyst converter (TWC) is used in order to convert the carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxide (Nox) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.
HINT: The heated oxygen sensor heater circuit uses a relay on the +B side of the circuit.
HINT:
- Sensor 1 refers to the sensor mounted before the TWC and is located near the engine assembly.
- Sensor 2 refers to the sensor mounted after the TWC and is located far from the engine assembly.
MONITOR DESCRIPTION
The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen concentration in the exhaust gas. If the zirconia element is at the proper temperature and difference of the oxygen concentration between the inside and outside surfaces of the sensor is large, the zirconia element will generate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated oxygen sensor and sets a DTC.
Heated oxygen sensor heater range check (P0037 and P0038):
- The ECM monitors the current applied to the heated oxygen sensor heater to check the heater for malfunctions. If the current is below the threshold value, the ECM will determine that there is an open circuit in the heater. If the current is above the threshold value, the ECM will determine that there is a short circuit in the heater.
Example:
The ECM sets DTC P0038 when the current in the heated oxygen sensor heater is more than 2 A. Conversely, when the heater current is less than 0.3 A, DTC P0037 is set.
Heated oxygen sensor heater performance (P0141):
- After the accumulated heater ON time exceeds 100 seconds, the ECM calculates the heater resistance using the battery voltage and the current applied to the heater. If the resistance is above the threshold value, the ECM will determine that there is a malfunction in the heated oxygen sensor heater and set DTC P0141.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
P0037:
P0038 (Condition A):
P0038 (Condition B):
P0141 (Heater performance monitor check):
TYPICAL MALFUNCTION THRESHOLDS
P0037:
P0038:
P0141 (Heater performance monitor check):
COMPONENT OPERATING RANGE
MONITOR RESULT
Refer to detailed information Mode 6 Data.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:
- Read freeze frame data using Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
- When DTC P0038 is detected, proceed to step 4 if the heater resistance is in normal range.
PROCEDURE
1. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)
(a) Disconnect the H13 heated oxygen sensor connector.
(b) Measure the resistance between the terminals of the heated oxygen sensor connector.
Standard resistance (Bank 1 sensor 2)::
(c) Reconnect the heated oxygen sensor connector.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
2. INSPECT INTEGRATION RELAY (EFI M RELAY)
(a) Remove the integration relay from the engine room relay block.
(b) Inspect the EFI M relay.
Standard resistance:
(c) Reinstall the integration relay.
NG -- REPLACE INTEGRATION RELAY
OK -- Continue to next step.
3. CHECK ECM (HT1B VOLTAGE)
(a) Turn the power switch ON (IG).
(b) Measure the voltage between the applicable terminals of the E4 and E6 ECM connectors.
Standard voltage:
OK -- REPLACE ECM
NG -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM AND EFI M RELAY)
(a) Check the harness and the connectors between the ECM and the heated oxygen sensor connectors.
(1) Disconnect the H13 heated oxygen sensor connector.
(2) Disconnect the E4 and E6 ECM connectors.
(3) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(4) Reconnect the heated oxygen sensor connector.
(5) Reconnect the ECM connectors.
(b) Check the harness and the connectors between the heated oxygen sensor connector and the EFI M relay.
(1) Disconnect the H13 heated oxygen sensor connector.
(2) Remove the integration relay from the engine room relay block.
(3) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(4) Reconnect the heated oxygen sensor connector.
(5) Reinstall the integration relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM